text: The ground state is believed to be a bent triplet, with two orthogonal sp hybrid orbitals singly occupied by unpaired spins. One electron occupies an orbital of sigma symmetry in the plane of the rings, while the other occupies an orbital of pi symmetry, which interacts with the pi systems of the adjacent aromatic rings (delocalization into the rings is minimal, since zero-field parameter D is high). The zero field splitting parameters predict a bond angle greater than 135°, and since the ideal bond geometry for cyclopentane carbons is about 109°, considerable ring strain causes the methylene sigma bonds to be bent. In the singlet state, the spin-paired electrons occupy the sp hybrid orbital, orthogonal to an empty p-orbital. Conversion of singlet to triplet fluorenylidene is achieved through intersystem crossing (ISC).